Radio receivers operate by receiving and processing an incoming radio frequency (RF) signal obtained from an antenna. Such processing includes performing analog front-end processing on the signal and downconverting the signal to a lower frequency signal. After downconverting the signal to a desired frequency range, additional processing is performed that results in a demodulated signal that can be output as desired audio signal. Different demodulation schemes are possible depending upon the type of received signal.
For frequency modulated (FM) signals, message content is modulated by way of modulating the frequency of the carrier signal with the message content. As such, on a receive end, a demodulator operates by a determining the modulation frequency to recover the original message content.
An FM demodulator operates on a received complex signal by calculating a change in angle over time. At low signal-to-noise ratio, additive noise can result in changes in the angle over time, which produce unwanted impulses in the demodulated signal. However, existing derivative-based impulse detection has some limitations. Example detectors do not completely remove the signal component and thus can false trigger in the presence of large undesired signals (large frequency deviation).
To remove impulsive noise, existing techniques typically are based on first and higher-order derivatives of the demodulator output to detect impulses. If the derivative is higher than a threshold, then affected samples are blanked and/or replaced using interpolation or extrapolation from adjacent samples. However, existing derivative-based impulse detection has some limitations.